Both fast acting and time delay fuses are well known in the fuse industry. One example of a typical time delay fuse is the fuse disclosed in U.S. Pat. No. 5,345,210 ('210 patent), the disclosure of which is incorporated herein by reference. The '210 patent, which is assigned to the assignee of the present application, is directed to a time delay fuse and various components of that time delay fuse. The fuse includes a housing made of an insulating material. First and second conductive terminals are secured to, and emerge from the opposite ends of the housing. The housing encloses a short-circuit fusible element, preferably a copper or copper alloy strip having a plurality of slots. The housing also encloses one or more rigid meltable fusible elements, preferably a plurality of solder bars. A body of resilient, compressible insulating material has at least one passageway through which each of the rigid meltable fusible elements extends. A quantity of pulverulent arc quenching material, preferably sand, is enclosed within the housing. When the rigid meltable fusible elements melt, the circuit through the fuse opens. In addition, the passageway which surrounded the rigid meltable fusible element collapses upon its melting. The closing of the passageway, and the sand enclosed within the housing aids in preventing arcs formed during the opening of the fuse from a condition known as "burn back," i.e., the movement of an arc through the length of the fuse. These features alone, however, are not always successful at eliminating potentially fuse damaging arcs generated within the fuse. The '210 patent does not disclose the use of an initially free-flowing silicone material as an arc barrier-forming body to prevent "burn-back."
Another time delay fuse is disclosed in U.S. Pat. No. 4,533,895 ('895 patent), the disclosure of which is incorporated herein by reference. The '895 patent, assigned to the assignee of the present invention, discloses a slow blowing or time delay fuse having one or more conducting fuse links for short-circuit blowout protection. The short-circuit blowout protecting fuse links are located at opposite longitudinal ends of the fuse in individual end chambers. These individual end chambers are contained and defined by a cup-shaped end cap and a washer. Each of these individual end chambers is filled with an arc-quenching filler, such as sand. The washer prevents sand from entering a central compartment or chamber.
While the end chambers of the '895 patent provide short-circuit blowout protection, the central compartment or chamber provides a more massive fuse link structure which provides blowout protection for prolonged, but relatively low, current overloads. The more massive fuse link structure within the central compartment includes a plunger, a plunger guide member, and a conically-shaped compressed coil spring. The '895 patent discloses a time delay blade terminal-type fuse which provides both short circuit protection and a time delayed protection under prolonged modest overload currents, however, the '895 patent does not disclose the use of an initially free-flowing silicone material as an arc barrier-forming body to protect against "burn-back" within the fuse.
Nevertheless, efforts have been made to include arc barrier-forming bodies to provide protection against "burn-back" in both fast acting and time delay fuses. These prior arc barrier-forming bodies have been formed from initially solid silicone rubber. A slit was cut in the solid silicone rubber body, and the fusible short-circuit element was manually inserted, and slid through the slit. Such a procedure, however, is time consuming and expensive. Also, during this procedure, the fusible short-circuit element was susceptible to axial movement which could damage not only the short-circuit element, but also the connections between components of the fuse. Prior arc barrier-forming bodies were also very difficult to slide onto fusible short-circuit elements that did not have generally flat, straight configurations. Moreover, because prior arc barrier-forming bodies did not adhere to the surface of the fusible short-circuit element, when the housing was filled with sand, the arc barrier-forming bodies had a tendency to move.
Other prior art of interest includes U.S. Pat. No. 5,245,308 ('308 patent), issued to Herbias, and assigned to the assignee of the present application. The '308 patent discloses a Class L fuse with an insulating, initially free-flowing sealant which acts as an arc barrier-forming body disposed at the end portions of the assembled housing. The '308 patent also fails to teach the use of an initially free-flowing material in the manner of the present invention. Particularly, the '308 patent fails to teach placing the arc barrier-forming body on an intermediate portion of the fusible short-circuit element in a Class R fuse.